Acute effect of the dual angiotensin-converting enzyme and neutral endopeptidase 24-11 inhibitor mixanpril on insulin sensitivity in obese Zucker rat

Neprilysin deficiency reduces hepatic gluconeogenesis in high fat-fed mice

Neprilysin is a peptidase that cleaves glucoregulatory peptides, including glucagon-like peptide-1 (GLP-1) and cholecystokinin (CCK). Some studies suggest that its inhibition in diabetes and/or obesity improves glycemia, and that this is associated with enhanced insulin secretion, glucose tolerance and insulin sensitivity. Whether reduced neprilysin activity also improves hepatic glucose metabolism has not been explored. We sought to determine whether genetic deletion of neprilysin suppresses hepatic glucose production (HGP) in high fat-fed mice. Nep+/+ and Nep-/- mice were fed high fat diet for 16 weeks, and then underwent a pyruvate tolerance test (PTT) to assess hepatic gluconeogenesis. Since glycogen breakdown in liver can also yield glucose, we assessed liver glycogen content in fasted and fed mice. In Nep-/- mice, glucose excursion during the PTT was reduced when compared to Nep+/+ mice. Further, liver glycogen levels were significantly greater in fasted but not fed Nep-/- versus Nep+/+ mice. Since gut-derived factors modulate HGP, we tested whether gut-selective inhibition of neprilysin could recapitulate the suppression of hepatic gluconeogenesis observed with whole-body inhibition, and this was indeed the case. Finally, the gut-derived neprilysin substrates, GLP-1 and CCK, are well-known to suppress HGP. Having previously demonstrated elevated plasma GLP-1 levels in Nep-/- mice, we now measured plasma CCK bioactivity and reveal an increase in Nep-/- versus Nep+/+ mice, suggesting GLP-1 and/or CCK may play a role in reducing HGP under conditions of neprilysin deficiency. In sum, neprilysin modulates hepatic gluconeogenesis and strategies to inhibit its activity may reduce HGP in type 2 diabetes and obesity.

Insulinotropic Effects of Neprilysin and/or Angiotensin Receptor Inhibition in Mice

Treatment of heart failure with the angiotensin receptor-neprilysin inhibitor sacubitril/valsartan improved glycemic control in individuals with type 2 diabetes. The relative contribution of neprilysin inhibition versus angiotensin II receptor antagonism to this glycemic benefit remains unknown. Thus, we sought to determine the relative effects of the neprilysin inhibitor sacubitril versus the angiotensin II receptor blocker valsartan on beta-cell function and glucose homeostasis in a mouse model of reduced first-phase insulin secretion, and whether any beneficial effects are additive/synergistic when combined in sacubitril/valsartan. High fat-fed C57BL/6J mice treated with low-dose streptozotocin (or vehicle) were followed for eight weeks on high fat diet alone or supplemented with sacubitril, valsartan or sacubitril/valsartan. Body weight and fed glucose levels were assessed weekly. At the end of the treatment period, insulin release in response to intravenous glucose, insulin sensitivity, and beta-cell mass were determined. Sacubitril and valsartan, but not sacubitril/valsartan, lowered fasting and fed glucose levels and increased insulin release in diabetic mice. None of the drugs altered insulin sensitivity or beta-cell mass, but all reduced body weight gain. Effects of the drugs on insulin release were reproduced in angiotensin II-treated islets from lean C57BL/6J mice, suggesting the insulin response to each of the drugs is due to a direct effect on islets and mechanisms therein. In summary, sacubitril and valsartan each exert beneficial insulinotropic, glycemic and weight-reducing effects in obese and/or diabetic mice when administered alone; however, when combined, mechanisms within the islet contribute to their inability to enhance insulin release.

Neprilysin inhibition improves intravenous but not oral glucose-mediated insulin secretion via GLP-1R signaling in mice with -cell dysfunction

Type 2 diabetes is associated with the upregulation of neprilysin, a peptidase capable of cleaving glucoregulatory peptides such as glucagon-like peptide-1 (GLP-1). In humans, use of the neprilysin inhibitor sacubitril in combination with an angiotensin II receptor blocker was associated with increased plasma GLP-1 levels and improved glycemic control. Whether neprilysin inhibition per se is mediating these effects remains unknown. We sought to determine whether pharmacological neprilysin inhibition on its own confers beneficial effects on glycemic status and β-cell function in a mouse model of reduced insulin secretion, and whether any such effects are dependent on GLP-1 receptor (GLP-1R) signaling. High-fat-fed male wild-type (Glp1r^+/+) and GLP-1R knockout (Glp1r^-/-) mice were treated with low-dose streptozotocin (STZ) to recapitulate type 2 diabetes-associated β-cell dysfunction, or vehicle as control. Mice were continued on high-fat diet alone or supplemented with the neprilysin inhibitor sacubitril for 8 wk. At the end of the study period, β-cell function was assessed by oral or intravenous glucose-tolerance test. Fasting and fed glucose were significantly lower in wild-type mice treated with sacubitril, although active GLP-1 levels and insulin secretion during oral glucose challenge were unchanged. In contrast, insulin secretion in response to intravenous glucose was significantly enhanced in sacubitril-treated wild-type mice, and this effect was blunted in Glp1r^-/- mice. Similarly, sacubitril enhanced insulin secretion in vitro in islets from STZ-treated Glp1r^+/+ but not Glp1r^-/- mice. Together, our data suggest the insulinotropic effects of pharmacological neprilysin inhibition in a mouse model of β-cell dysfunction are mediated via intra-islet GLP-1R signaling.NEW & NOTEWORTHY The neprilysin inhibitor, sacubitril, improves glycemic status in a mouse model of reduced insulin secretion. Sacubitril enhances intravenous but not oral glucose-mediated insulin secretion. The increased glucose-mediated insulin secretion is GLP-1 receptor-dependent. Neprilysin inhibition does not raise postprandial circulating active GLP-1 levels.

Modulation of insulin resistance by renin angiotensin system inhibitors: implications for cardiovascular prevention

Insulin resistance (IR) and the related hyperinsulinamia play a key role in the genesis and progression of the continuum of cardiovascular (CV) disease. Thus, it is reasonable to pursue in primary and secondary CV prevention, the pharmacological strategies that are capable to interfere with the development of IR. The renin-angiotensin-aldosterone system (RAAS) plays an important role in the pathogenesis of IR. In particular, angiotensin II (Ang II) through the generation of reactive oxygen species, induces a low grade of inflammation, which impairs the insulin signal transduction. The angiotensin converting enzyme (ACE) inhibitors are effective not only as blood pressure-lowering agents, but also as modulators of metabolic abnormalities. Indeed, experimental evidence indicates that in animal models of IR, ACE inhibitors are capable to ameliorate the insulin sensitivity. The Ang II receptor blockers (ARBs) modulate the peroxisome proliferator-activated receptor (PPAR)-γ activity. PPARâ€"γ is a transcription factor that controls the gene expression of several key enzymes of glucose metabolism. A further mechanism that accounts for the favorable metabolic properties of ARBs is the capability to modulate the hypothalamicâ€"pituitary-adrenal (HPA) axis. The available clinical evidence is consistent with the concept that both ACE inhibitors and ARBs are able to interfere with the development of IR and its consequences like type 2 diabetes. In addition, pharmacological inhibition of the RAAS has favourable effects on dyslipidaemias, metabolic syndrome and obesity. Therefore, the pharmacological antagonism of the RAAS, nowadays, represents the first choice in the prevention of cardio-metabolic diseases.

Bradykinin B2 Receptor Signaling Increases Glucose Uptake and Oxidation: Evidence and Open Questions

The Kinin B2 receptor (B2R) is classically involved in vasodilation and inflammatory responses. However, through the observation of hypoglycemic effects of Angiotensin-I-Converting Enzyme (ACE) inhibitors, this protein has been related to metabolic glucose modulation in physiological and pathophysiological contexts. Although several studies have evaluated this matter, the different methodologies and models employed, combined with the distinct target organs, results in a challenge to summarize and apply the knowledge in this field. Therefore, this review aims to compile human and animal data in order to provide a big picture about what is already known regarding B2R and glucose metabolism, as well to suggest pending investigation issues aiming at evaluating the role of B2R in relation to glucose metabolism in homeostatic situations and metabolic disturbances. The data indicate that B2R signaling is involved mainly in glucose uptake in skeletal muscle and adipose tissue, acting as a synergic player beside insulin. However, most data indicate that B2R induces increased glucose oxidation, instead of storage, via activation of a broad signaling cascade involving Nitric Oxide (NO) and cyclic-GMP dependent protein kinase (PKG). Additionally, we highlight that this modulation is impaired in metabolic disturbances such as diabetes and obesity, and we provide a hypothetic mechanism to explain this blockade in light of literature data provided for this review, as well as other authors.

Enhancement of Amyloid β1-43 Production in the Lens Epithelium of Japanese Type 2 Diabetic Patients

We investigated whether the accumulation of amyloid β-protein (Aβ) is enhanced in the lenses of diabetic patients. Lens epithelium samples were collected from Japanese patients during cataract surgery, and the Aβ levels and gene expression of Aβ-producing and -degrading enzymes in the samples were measured by ELISA and real-time RT-PCR, respectively. The Aβ_1–43 levels in lenses of non-diabetic patients were low (0.11 pmol/g protein), while the levels in lenses of diabetic patients were significantly (6-fold) higher. Moreover, the Aβ_1–43/total-Aβ ratio in the lenses of diabetic patients was also significantly higher than non-diabetic patients (p < 0.05). In addition, the mRNA levels for Aβ-producing enzymes were also enhanced in the lenses of diabetic patients. In contrast to the results for Aβ-producing enzymes, the mRNAs for the Aβ-degrading enzymes in the lenses of diabetic patients were significantly lower than in non-diabetic patients (p < 0.05). Furthermore, Aβ_1–43/total-Aβ ratio in lenses was found to increase with plasma glucose level. In conclusion, these results suggest that high glucose levels cause both an increase in Aβ production and a decrease in Aβ degradation, and these changes lead to the enhancement in Aβ_1–43 accumulation in the lenses of diabetic patients. These findings are useful for developing therapies for diabetic cataracts and for developing anti-cataract drugs.

Soluble neprilysin: A versatile biomarker for heart failure, cardiovascular diseases and diabetic complications-A systematic review

The potential role of soluble neprilysin (sNEP) as a biomarker has been poorly documented. Hence, the present systematic review emphasizes to explore sNEP as an emerging biomarker for heart failure (HF), cardiovascular diseases, diabetic kidney diseases, and so on. A systematic review was performed using an online database search in PubMed, Science Direct, Scopus, and Cochrane Library. Articles reporting biomarker's performance to diagnose various diseases in human participants were included. The results of the search outcome were 4723 articles. Based on the inclusion criteria of the systematic review, finally, 12 articles fulfilled the selection criteria. In these studies, 8 cohort study, 2 cross-sectional study, 1 case-control, and 1 prospective cohort study were identified. All these studies clearly suggested sNEP as a potential biomarker for diagnosis of various diseases (HF, cardiovascular diseases, diabetic kidney diseases, metabolic syndrome). sNEP may be a potential biomarker for HF, cardiovascular diseases, diabetic kidney disease, and so on.

Potential mechanisms of beneficial effect of sacubitril/valsartan on glycemic control

Heart failure (HF) and diabetes mellitus (DM) frequently coexist, with a prevalence of DM of 35-40% in patients with HF, independent of the level of impairment of the ejection fraction (EF). Furthermore, DM is considered a strong independent risk factor for the progression of HF with either preserved or reduced EF and is associated with poor prognosis. The ability of neprilysin inhibitors to elevate levels of biologically active natriuretic peptides has made them a potential therapeutic approach in HF. In the Prospective comparison of ARNi with ACEi to Determine Impact on Global Mortality and morbidity in Heart Failure (PARADIGM-HF) trial, a dual-acting angiotensin-receptor-neprilysin inhibitor, sacubitril/valsartan was superior to enalapril in reducing the risks of death and HF hospitalization in patients with HF with reduced EF. In addition, in a post-hoc analysis of this trial, among patients with DM, treatment with sacubitril/valsartan resulted in improved glycemic control compared with enalapril. Also, there are additional studies suggesting beneficial metabolic effects of this class of drugs. In this review we discuss potential mechanisms of sacubitril/valsartan effect on glycemic control. Sacubitril/valsartan concomitantly blocks the renin-angiotensin system and inhibits neprilysin, a ubiquitous enzyme responsible for the breakdown of more than 50 vasoactive peptides, including the biologically active natriuretic peptides, bradykinin, angiotensin I and II, endothelin 1, glucagon, glucagon-like peptide-1, insulin-B chain, and others. There are a number of potential mechanisms by which inhibition of neprilysin may lead to improvement in glycemic control, with most evidence suggesting modulation of neprilysin circulating substrates. Although there is some evidence suggesting the improvement of glucose metabolism by renin-angiotensin system inhibition, this effect is most likely modest. As these mechanisms are not fully understood, detailed mechanistic studies, as well as large randomized clinical trials in patients with DM, are needed to further clarify beneficial metabolic properties of sacubitril/valsartan.

Neprilysin inhibition: a new therapeutic option for type 2 diabetes?

Neprilysin is a widely expressed peptidase with broad substrate specificity that preferentially hydrolyses oligopeptide substrates, many of which regulate the cardiovascular, nervous and immune systems. Emerging evidence suggests that neprilysin also hydrolyses peptides that play an important role in glucose metabolism. In recent studies in humans, a dual angiotensin receptor-neprilysin inhibitor (ARNi) improved glycaemic control and insulin sensitivity in individuals with type 2 diabetes and/or obesity. Moreover, preclinical studies have also reported that neprilysin inhibition, alone or in combination with renin-angiotensin system blockers, elicits beneficial effects on glucose homeostasis. Since neprilysin inhibitors have been approved for the treatment of heart failure, their repurposing for treating type 2 diabetes would provide a novel therapeutic strategy. In this review, we evaluate existing evidence from preclinical and clinical studies in which neprilysin is deleted/inhibited, we highlight potential mechanisms underlying the beneficial glycaemic effects of neprilysin inhibition, and discuss possible deleterious effects that may limit the efficacy and safety of neprilysin inhibitors in the clinic. We also review the favourable impact neprilysin inhibition can have on diabetic complications, in addition to glucose control. Finally, we conclude that neprilysin inhibitors may be a useful therapeutic option for treating type 2 diabetes; however, their combination with angiotensin II receptor blockers is needed to circumvent deleterious consequences of neprilysin inhibition alone.

Obesity and aging affects skeletal muscle renin-angiotensin system and myosin heavy chain proportions in pre-diabetic Zucker rats

There is a gap in the knowledge regarding regulation of local renin-angiotensin system (RAS) in skeletal muscle during development of obesity and insulin resistance in vivo. This study evaluates the obesity- and age-related changes in the expression of local RAS components. Since RAS affects skeletal muscle remodelling, we also evaluated the muscle fibre type composition, defined by myosin heavy chain (MyHC) mRNAs and protein content. Gene expressions were determined by qPCR and/or Western blot analysis in musculus quadriceps of 3- and 8-month-old male obese Zucker rats and their lean controls. The enzymatic activity of aminopeptidase A (APA) was determined flourometrically. Activation of renin receptor (ReR)/promyelocytic leukaemia zinc finger (PLZF) negative feedback mechanism was observed in obesity. The expression of angiotensinogen and AT1 was downregulated by obesity, while neutral endopeptidase and AT2 expressions were upregulated in obese rats with aging. Skeletal muscle APA activity was decreased by obesity, which negatively correlated with the increased plasma APA activity and plasma cholesterol. The expression of angiotensin-converting enzyme (ACE) positively correlated with MyHC mRNAs characteristic for fast-twitch muscle fibres. The obesity- and age-related alterations in the expression of both classical and alternative RAS components suggest an onset of a new equilibrium between ACE/AngII/AT1 and ACE2/Ang1-7/Mas at lower level accompanied by increased renin/ReR/PLZF activation. Increased APA release from the skeletal muscle in obesity might contribute to increased plasma APA activity. There is a link between reduced ACE expression and altered muscle MyHC proportion in obesity and aging.

Neprilysin Deficiency Is Associated With Expansion of Islet β-Cell Mass in High Fat-Fed Mice

Neprilysin (NEP) is an endopeptidase known to modulate nervous, cardiovascular, and immune systems via inactivation of regulatory peptides. In addition, it may also contribute to impaired glucose homeostasis as observed in type 2 diabetes (T2D). Specifically, we and others have shown that NEP is upregulated under conditions associated with T2D, whereas NEP deficiency and/or inhibition improves glucose homeostasis via enhanced glucose tolerance, insulin sensitivity, and pancreatic β-cell function. Whether increased β-cell mass also occurs with lack of NEP activity is unknown. We sought to determine whether NEP deficiency confers beneficial effects on β- and α-cell mass in a mouse model of impaired glucose homeostasis. Wild-type and NEP^-/- mice were fed low- or high-fat diet for 16 weeks, after which pancreatic β- and α-cell mass were assessed by immunostaining for insulin and glucagon, respectively. Following low-fat feeding, NEP^-/- mice exhibited lower β- and α-cell mass compared with wild-type controls. A high-fat diet had no effect on these parameters in wild-type mice, but in NEP^-/- mice, it resulted in the expansion of β-cell mass. Our findings support a role for NEP in modulating β-cell mass, making it an attractive T2D drug target that acts via multiple mechanisms to affect glucose homeostasis.

Natriuretic peptides in the control of lipid metabolism and insulin sensitivity

Natriuretic peptides have long been known for their cardiovascular function. However, a growing body of evidence emphasizes the role of natriuretic peptides in human substrate and energy metabolism, thereby connecting the heart with several insulin-sensitive organs like adipose tissue, skeletal muscle and liver. Obesity may be associated with an impaired regulation of the natriuretic peptide system, also indicated as a natriuretic handicap. Evidence points towards a contribution of this natriuretic handicap to the development of obesity, type 2 diabetes mellitus and cardiometabolic complications, although the causal relationship is not fully understood. Nevertheless, targeting the natriuretic peptide pathway may improve metabolic health in obesity and type 2 diabetes mellitus. This review will focus on current literature regarding the metabolic roles of natriuretic peptides with emphasis on lipid metabolism and insulin sensitivity. Furthermore, it will be discussed how exercise and lifestyle intervention may modulate the natriuretic peptide-related metabolic effects.

Improved glycaemia in high-fat-fed neprilysin-deficient mice is associated with reduced DPP-4 activity and increased active GLP-1 levels

AIM/HYPOTHESIS

Neprilysin, a widely expressed peptidase, is upregulated in metabolically altered states such as obesity and type 2 diabetes. Like dipeptidyl peptidase-4 (DPP-4), neprilysin can degrade and inactivate the insulinotropic peptide glucagon-like peptide-1 (GLP-1). Thus, we investigated whether neprilysin deficiency enhances active GLP-1 levels and improves glycaemia in a mouse model of high fat feeding.

METHODS

Nep ^+/+ and Nep ^-/- mice were fed a 60% fat diet for 16 weeks, after which active GLP-1 and DPP-4 activity levels were measured, as were glucose, insulin and C-peptide levels during an OGTT. Insulin sensitivity was assessed using an insulin tolerance test.

RESULTS

High-fat-fed Nep ^-/- mice exhibited elevated active GLP-1 levels (5.8 ± 1.1 vs 3.5 ± 0.8 pmol/l, p < 0.05) in association with improved glucose tolerance, insulin sensitivity and beta cell function compared with high-fat-fed Nep ^+/+ mice. In addition, plasma DPP-4 activity was lower in high-fat-fed Nep ^-/- mice (7.4 ± 1.0 vs 10.7 ± 1.3 nmol ml^-1 min^-1, p < 0.05). No difference in insulin:C-peptide ratio was observed between Nep ^-/- and Nep ^+/+ mice, suggesting that improved glycaemia does not result from changes in insulin clearance.

CONCLUSIONS/INTERPRETATION

Under conditions of increased dietary fat, an improved glycaemic status in neprilysin-deficient mice is associated with elevated active GLP-1 levels, reduced plasma DPP-4 activity and improved beta cell function. Thus, neprilysin inhibition may be a novel treatment strategy for type 2 diabetes.

Metabolic Syndrome as a Risk Factor for Alzheimer's Disease: Is Aβ a Crucial Factor in Both Pathologies?

SIGNIFICANCE

Recently, chronic degenerative diseases have become one of the main health problems worldwide. That is the case of Alzheimer's disease (AD) and metabolic syndrome (MetS), whose expression can be influenced by different risk factors. Recent Advances: In recent decades, it has been widely described that MetS increases the risk of cognitive impairment and dementia. MetS pathogenesis involves several vascular risk factors such as diabetes, dyslipidemia, hypertension, and insulin resistance (I/R).

CRITICAL ISSUES

Reported evidence shows that vascular risk factors are associated with AD, particularly in the development of protein aggregation, inflammation, oxidative stress, neuronal dysfunction, and disturbances in signaling pathways, with insulin receptor signaling being a common alteration between MetS and AD.

FUTURE DIRECTIONS

Insulin signaling has been involved in tau phosphorylation and amyloid β (Aβ) metabolism. However, it has also been demonstrated that Aβ oligomers can bind to insulin receptors, triggering their internalization, decreasing neuron responsiveness to insulin, and promoting insulin I/R. Thus, it could be argued that Aβ could be a convergent factor in the development of both pathologies. Antioxid. Redox Signal. 26, 542-560.

Microvascular responsiveness in obesity: implications for therapeutic intervention

Obesity has detrimental effects on the microcirculation. Functional changes in microvascular responsiveness may increase the risk of developing cardiovascular complications in obese patients. Emerging evidence indicates that selective therapeutic targeting of the microvessels may prevent life-threatening obesity-related vascular complications, such as ischaemic heart disease, heart failure and hypertension. It is also plausible that alterations in adipose tissue microcirculation contribute to the development of obesity. Therefore, targeting adipose tissue arterioles could represent a novel approach to reducing obesity. This review aims to examine recent studies that have been focused on vasomotor dysfunction of resistance arteries in obese humans and animal models of obesity. Particularly, findings in coronary resistance arteries are contrasted to those obtained in other vascular beds. We provide examples of therapeutic attempts, such as use of statins, ACE inhibitors and insulin sensitizers to prevent obesity-related microvascular complications. We further identify some of the important challenges and opportunities going forward.

LINKED ARTICLES

This article is part of a themed section on Fat and Vascular Responsiveness. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.165.issue-3.

Effect of Inhibition of Angiotensin-Converting Enzyme and/or Neutral Endopeptidase on Neuropathy in High-Fat-Fed C57Bl/6J Mice

We have demonstrated that treating diet-induced obese (DIO) mice with the vasopeptidase inhibitor ilepatril improved neural function. Vasopeptidase inhibitors block angiotensin-converting enzyme (ACE) and neutral endopeptidase (NEP) activity. We propose that increased activity of ACE and NEP contributes to pathophysiology of DIO. To address this issue C57Bl/6J mice or mice deficient in NEP were fed a high-fat diet and treated with ilepatril, enalapril, ACE inhibitor, or candoxatril, NEP inhibitor, using both prevention and intervention protocols. Endpoints included glucose utilization and neural function determination. In the prevention study glucose tolerance was impaired in DIO C57Bl/6J mice and improved with ilepatril or enalapril. Sensory nerve conduction velocity, thermal nociception, and intraepidermal nerve fiber density were impaired in DIO C57Bl/6J mice and improved with ilepatril or candoxatril. In the intervention study only enalapril improved glucose tolerance. Sensory nerve conduction velocity and intraepidermal nerve fiber density were improved by all three treatments, whereas thermal nociception was improved by ilepatril or candoxatril. In NEP-deficient mice DIO impaired glucose utilization and this was improved with enalapril. Nerve function was not impaired by DIO in NEP-deficient mice. These studies suggest that ACE and NEP play a role in pathophysiology associated with DIO.

Effect of inhibition of angiotensin converting enzyme and/or neutral endopeptidase on vascular and neural complications in high fat fed/low dose streptozotocin-diabetic rats

Treating high fat fed/low dose streptozotocin-diabetic rats; model of type 2 diabetes, with ilepatril (vasopeptidase inhibitor, blocks neutral endopeptidase (NEP) and angiotensin converting enzyme (ACE)) improved vascular and neural functions. Next, studies were performed to determine the individual effect of inhibition of NEP and ACE on diabetes-induced vascular and neural dysfunctions. High fat fed rats (8 weeks) were treated with 30 mg/kg streptozotocin (i.p.) and after 4 additional weeks, were treated for 12 weeks with ilepatril, enalapril (ACE inhibitor) or candoxatril (NEP inhibitor) followed by analysis of vascular and neural functions. Glucose clearance was impaired in diabetic rats and was not improved with treatment although treatment with ilepatril or candoxatril partially improved insulin stimulated glucose uptake by isolated soleus muscle. Diabetes caused slowing of motor and sensory nerve conduction, thermal hypoalgesia, reduction in intraepidermal nerve fiber (IENF) profiles and impairment in vascular relaxation to acetylcholine and calcitonin gene-related peptide (CGRP) in epineurial arterioles of the sciatic nerve. Inhibition of NEP improved nerve conduction velocity and inhibition of NEP or ACE improved thermal sensitivity and protected IENF density. Ilepatril and candoxatril treatments of diabetic rats were efficacious in improving vascular responsiveness to acetylcholine in epineurial arterioles; whereas all three treatments improved vascular response to CGRP. These studies suggest that inhibition of NEP and ACE activity is an effective approach for treatment of type 2 diabetes neural and vascular complications.

Effect of treatment of high fat fed/low dose streptozotocin-diabetic rats with Ilepatril on vascular and neural complications

We have previously shown that treating streptozotocin-induced diabetic rats, an animal model of type 1 diabetes, with Ilepatril (an inhibitor of neutral endopeptidase and angiotensin converting enzyme (ACE)) improves vascular and neural functions. In this study we sought to determine the effect of Ilepatril treatment of high fat fed/low dose streptozotocin-diabetic rats, a model for type 2 diabetes, on vascular and neural complications. Following 8 weeks on a high fat diet rats were treated with 30 mg/kg streptozotocin (i.p.) and after 4 additional weeks a group of these rats was treated for 12 weeks with Ilepatril followed by analysis of neural and vascular functions. Included in these studies were age-matched control rats and rats fed a high fat diet and treated with or without Ilepatril. Diabetic and diet induced obese rats have characteristics of insulin resistance, slowing of nerve conduction velocity, thermal hypoalgesia, reduction in intraepidermal nerve fiber density in the hindpaw and impairment in vascular relaxation to acetylcholine and calcitonin gene-related peptide in epineurial arterioles of the sciatic nerve. Treatment with Ilepatril was efficacious in improving all of these endpoints although improvement of insulin resistance in diabetic rats was minimal. These studies suggest that dual inhibition of angiotensin converting enzyme and neutral endopeptidase activity of type 2 diabetic rats is an effective approach for treatment of diabetic neural and vascular complications.

Effect of Treatment of Sprague Dawley Rats with AVE7688, Enalapril, or Candoxatril on Diet-Induced Obesity

The objective of this study was to determine the effect of AVE7688, a drug that inhibits both angiotensin converting enzyme (ACE) and neutral endopeptidase (NEP) activity, on neural and vascular defects caused by diet induced obesity (DIO). Rats at 12 weeks of age were fed a standard or high fat diet with or without AVE7688 for 24 weeks. DIO rats had impaired glucose tolerance and developed sensory neuropathy. Vascular relaxation to acetylcholine and calcitonin gene-related peptide was decreased in epineurial arterioles of DIO rats. Rats fed a high fat diet containing AVE7688 did not become obese and vascular and sensory nerve dysfunction and impaired glucose tolerance were improved. DIO is associated with increased expression of NEP in epineurial arterioles. NEP degrades vasoactive peptides which may explain the decrease in neurovascular function in DIO.

Neprilysin, obesity and the metabolic syndrome

Objective

Neprilysin (NEP), a zinc metallo-endopeptidase, has a role in blood pressure control and lipid metabolism. The present study tested the hypothesis that NEP is associated with insulin resistance and features of the metabolic syndrome (MetS) in a study of 318 healthy human subjects and in murine obesity and investigated NEP production by adipocytes in-vitro.

Methods and Results

In 318 white European males, plasma NEP was elevated in the MetS and increased progressively with increasing MetS components. Plasma NEP activity correlated with insulin, homeostasis model assessment and body mass index in all subjects (p<0.01). Quantitative RT-PCR and Western blotting showed that in human pre-adipocytes NEP expression is upregulated 25-30 fold during differentiation into adipocytes. Microarray analysis of mRNA from differentiated human adipocytes confirmed high NEP expression comparable to adiponectin and plasminogen activator inhibitor-1. In a murine model of diet-induced insulin resistance, plasma NEP levels were significantly higher in high fat diet (HFD)-fed compared with normal chow diet (NCD)-fed animals (1642±529 and 820±487 pg/μl, respectively; p<0.01). Tissue NEP was increased in mesenteric fat in HFD compared with NCD-fed mice (p<0.05). NEP knock out mice did not display any changes in insulin resistance, glucose tolerance or body and epididymal fat pad weight compared to wild type mice.

Conclusions

In humans, NEP activity correlated with body mass index and measures of insulin resistance with increasing levels in subjects with multiple cardiovascular risk factors. NEP protein production in human adipocytes increased during cell differentiation and plasma and adipose tissue levels of NEP were increased in obese insulin resistant mice. Our results indicate that NEP associates with cardio-metabolic risk in the presence of insulin resistance and increases in obesity.

Vasopeptidase inhibitor ilepatril (AVE7688) prevents obesity- and diabetes-induced neuropathy in C57Bl/6J mice

Previously we demonstrated that inhibition of neutral endopeptidase (NEP), a protease that degrades vaso- and neuro-active peptides, and angiotensin converting enzyme (ACE) with a vasopeptidase inhibitor improves vascular and neural function in diabetic rat models. The purpose of this study was to determine whether inhibition of NEP and ACE or deletion of NEP provides protection from nerve impairment caused by diabetes or diet induced obesity (DIO). To determine the role of NEP and ACE inhibition in neuropathy related to insulin-deficient diabetes or DIO we used C57Bl/6J mice treated with AVE7688, a vasopeptidase inhibitor, or NEP deficient (-/-) mice. Mice at 12 weeks of age were fed a high fat diet for 12 weeks or were diabetic for duration of 12 weeks following a single injection of high dose streptozotocin. Both a prevention and intervention protocol was used for AVE7688 treatment. Glucose utilization was impaired in DIO C57Bl/6J and NEP -/- mice. However, treating DIO C57Bl/6J or NEP -/- mice with AVE7688 improved glucose tolerance. Thermal hypoalgesia and nerve conduction slowing were present in both streptozotocin-diabetic and DIO C57Bl/6J mice but not in AVE7688 treated C57Bl/6J mice or NEP -/- mice exposed to either streptozotocin-induced diabetes or a high fat diet. Intraepidermal nerve fiber (IENF) profiles were decreased in the hindpaw of C57Bl/6J diabetic or DIO mice and this improved when the mice were treated with AVE7688. IENF profiles were not decreased in diabetic or DIO NEP (-/-) mice. These studies suggest that NEP plays a role in regulating nerve function in insulin-deficient diabetes and DIO.

Vascular and neural dysfunctions in obese Zucker rats: effect of AVE7688

The purpose of this study was to determine whether AVE7688 a drug that inhibits both angiotensin converting enzyme and neutral endopeptidase activity protects vascular and nerve functions in an animal model of metabolic syndrome. Obese Zucker rats at 20 weeks of age were treated for 12 weeks with AVE7688. Vasodilation in epineurial arterioles was measured by videomicroscopy and nerve conduction velocity was measured following electrical stimulation. Treatment with AVE7688 improved vascular relaxation in response to acetylcholine and motor and sensory nerve conduction velocity. In obese Zucker rats superoxide levels and nitrotyrosine staining were elevated in the aorta and treatment corrected both conditions. Obese Zucker rats were hypoalgesic in response to a thermal stimulus and demonstrated signs of impaired tactile response and both conditions were significantly improved with treatment. Even though obese Zucker rats are normoglycemic vascular and neural dysfunctions develop with age and can be improved by treatment with AVE7688.

Blocking the renin-angiotensin-aldosterone system to prevent diabetes mellitus

Type 2 diabetes mellitus (DM) is increasing around the world, and the public health impact of DM, driven largely by cardiovascular disease complications, underpins the importance of continued efforts toward primary prevention of DM. Only a few interventions have been shown to prevent DM, with none of them yet proven to improve cardiovascular risk commensurately. Accumulating evidence suggest that drugs that block the renin-angiotensin-aldosterone system (RAAS), many of which have proven cardiovascular disease (CVD) benefit, also have favourable effects on parameters of glucose metabolism and incident diabetes. Here we review the evidence accumulated to date from animal studies, clinical mechanistic studies and clinical trials regarding the effect of RAAS inhibition and incident DM.

Treating insulin resistance: future prospects

Insulin resistance typically reflects multiple defects of insulin receptor and post-receptor signalling that impair a diverse range of metabolic and vascular actions. Many potential intervention targets and compounds with therapeutic activity have been described. Proof of principle for a non-peptide insulin mimetic has been demonstrated by specific activation of the intracellular B-subunit of the insulin receptor. Potentiation of insulin action has been achieved with agents that enhance phosphorylation and prolong the tyrosine kinase activity of the insulin receptor and its protein substrates after activation by insulin. These include inhibitors of phosphatases and serine kinases that normally prevent or terminate tyrosine kinase signalling. Additional approaches involve increasing the activity of phosphatidylinositol 3-kinase and other downstream components of the insulin signalling pathways. Experimental interventions to remove signalling defects caused by cytokines, certain adipocyte hormones, excess fatty acids, glucotoxicity and negative feedback by distal signalling steps have also indicated therapeutic possibilities. Several hormones, metabolic enzymes, minerals, co-factors and transcription co-activators have shown insulin-sensitising potential. Since insulin resistance affects many metabolic and cardiovascular diseases, it provides an opportunity for simultaneous therapeutic attack on a broad front.

The metabolic syndrome: role of skeletal muscle metabolism

Skeletal muscle constitutes the largest insulin-sensitive tissue in the body and is the primary site for insulin-stimulated glucose utilization. Skeletal muscle resistance to insulin is fundamental to the metabolic dysregulation associated with obesity and physical inactivity, and contributes to the development of the metabolic syndrome (MS). The inability to efficiently take up and store fuel, and to transition from fat to glucose as the primary source of fuel during times of caloric abundance (high insulin) or scarcity (low insulin) has been termed metabolic inflexibility which contributes to a whole body metabolic dysregulation and cardiovascular risk. Potential mechanisms contributing to reduced insulin signaling and action in skeletal muscle includes adipose tissue expansion and increased inflammatory adipokines, increased renin-angiotensin-aldosterone system (RAAS) activity, decreases in muscle mitochondrial oxidative capacity, increased intramuscular lipid accumulation, and increased reactive oxygen species. Future research is focused upon understanding these and other potential mechanisms in order to identify therapeutic targets for reducing MS risk. Strategies will include adequate physical activity and maintaining a healthy weight, but may also require specific pharmacologic interventions.

Neutral endopeptidase 24.11 and dipeptidyl peptidase IV are both mediators of the degradation of glucagon-like peptide 1 in the anaesthetised pig

AIMS/HYPOTHESIS

The incretin hormone glucagon-like peptide 1 (GLP-1) has antihyperglycaemic effects, but its therapeutic usefulness is limited by its metabolic instability. Dipeptidyl peptidase IV (DPP-IV) is established as the primary inactivating enzyme, but the roles of other enzymes remain unclear.

METHODS

The effect of candoxatril, a selective inhibitor of neutral endopeptidase (NEP) 24.11, on GLP-1 pharmacokinetics/pharmacodynamics with or without DPP-IV inhibition was examined in anaesthetised pigs.

RESULTS

During GLP-1 infusion, candoxatril doubled C-terminal immunoreactivity, improving the pharmacokinetics (t(1/2) 2.3+/-0.1 to 8.8+/-1.2 min; metabolic clearance rate [MCR] 20.4+/-3.4 to 4.8+/-0.4 ml.kg(-1). min(-1); p<0.01), but had no effect upon intact GLP-1 (t(1/2) 1.4+/-0.1 to 1.6+/-0.1 min; MCR 47.9+/-8.0 to 38.8+/-5.0 ml.kg(-1).min(-1)). Insulin responses to intravenous glucose were unaffected by candoxatril, but glucose tolerance was improved (DeltaAUC(min 27-87) 118+/-5 to 74+/-14 min.mmol.l(-1); glucose elimination rate [k] 6.6+/-0.5 to 8.6+/-0.5%; p<0.05). When candoxatril was co-administered with valine pyrrolidide (a DPP-IV inhibitor), changes in C-terminal GLP-1 pharmacokinetics mirrored those seen when candoxatril alone was administered (t(1/2) 2.7+/-0.3 and 7.7+/-0.8 min; MCR 17.3+/-2.6 and 6.5+/-0.8 ml.kg(-1).min(-1) for valine pyrrolidide without and with candoxatril, respectively). However, intact GLP-1 pharmacokinetics were improved (t(1/2) 2.8+/-0.3 and 7.5+/-0.6 min; MCR 18.3+/-0.6 and 9.4+/-0.9 ml.kg(-1).min(-1); p<0.02), potentiating the antihyperglycaemic/insulinotropic effects of GLP-1 (glucose deltaAUC(min 27- 87) 103+/-8 to 62+/-14 min.mmol.l(-1); k 6.8+/-0.4 to 11.4+/-1.4%; insulin deltaAUC(min 27-87) 3,680+/-738 to 7,201+/-1,183 min.pmol.l(-1); p<0.05).

CONCLUSIONS/INTERPRETATION

This study confirms a role for NEP-24.11 in GLP-1 metabolism in vivo, suggesting that up to 50% of GLP-1 entering the circulation may be degraded by NEP-24.11. Furthermore, combined inhibition of DPP-IV and NEP-24.11 is superior to DPP-IV inhibition alone in preserving intact GLP-1, which raises the possibility that the combination has therapeutic potential.

Vasopeptidase inhibitors: will they have a role in clinical practice?

The human cardiovascular system is regulated by haemodynamic, neurohumoral and structural mechanisms. The endothelium and the neurohumoral system play a key role in modulating both vascular tone and structure by producing vasoactive substances, and in the modulation of blood cell adhesion. Although the neurohormonal systems are essential in vascular homeostasis, they become maladaptive in conditions such as hypertension, coronary disease and heart failure. The clinical success of blocking the renin-angiotensin system by angiotensin converting enzyme (ACE)-inhibitors and the sympathetic nerve system by beta-blockers demonstrates the importance of neurohumoral blockade. The inadequate effect of angiotensin converting enzyme (ACE) or neutral endopeptidase (NEP) inhibitor monotherapy seen in some patients treated for hypertension or congestive heart failure, and the promising effect seen after their combination, led to the development of drugs that simultaneously inhibit both enzyme systems. Neutral endopeptidase, like ACE, is an endothelial cell surface zinc metallopeptidase with similar structure and catalytic site to ACE. NEP is the major enzymatic pathway for degradation of natriuretic peptides. The natriuretic peptide system can be viewed as the endogenous inhibitor of the renin angiotensin system. The dual metalloprotease inhibitors of ACE and NEP, called vasopeptidase inhibitors therefore represent a new and attractive therapeutic strategy for the treatment of cardiovascular disease. The ability to add incremental benefit over already proven therapy, with an acceptable side-effect profile however, is questionable in this new class of agents.

Effect of imidapril, an angiotensin-converting enzyme inhibitor, on fructose-induced insulin resistance in rats

The effect of imidapril, an angiotensin-converting enzyme (ACE) inhibitor, on insulin resistance was studied in high-fructose-fed rats. A sequential hyperinsulinemic euglycemic clamp procedure (insulin infusion rates: 3 and 30 mU/kg BW/min) was employed in 15 high-fructose-fed rats and 10 normal chow-fed rats under the awake condition. Five of the high-fructose-fed and five of the normal chow-fed rats, respectively, were continuously given imidapril (5 mg/kg BW/min) or saline during the two-step euglycemic clamp study. Furthermore, both imidapril and L-NMMA were infused in another 5 high-fructose-fed rats during the low-dose insulin clamp. Glucose infusion rate (GIR) was regarded as an index of the whole-body insulin action. In the low-dose insulin infusion, the high-fructose feeding resulted in a marked decrease in GIR (p<0.05). Imidapril infusion significantly raised the GIRs in the high-fructose-fed rats (p<0.05). There was no significant difference in GIRs between the chow-fed rats and the imidapril-infused rats with high-fructose diet. In the high-fructose-fed rats, L-NMMA abolished the increase in GIR induced by imidapril (p<0.05). Imidapril did not significantly change the GIRs in the chow-fed rats. In the high-dose insulin infusion, no significant difference in GIR was found among the chow-fed rats, the chow-fed rats given imidapril, the high-fructose-fed rats, and the high-fructose-fed rats given imidapril. These results suggest that, in insulin-resistant rats induced by the high-fructose feeding, an ACE inhibitor, such as imidapril, can improve the whole-body insulin-mediated glucose disposal and that this effect of imidapril is essentially linked to increased activation of NO-pathway.

Modulation of metabolic control by angiotensin converting enzyme (ACE) inhibition

Angiotensin converting enzyme (ACE) inhibitors are a widely used intervention for blood pressure control, and are particularly beneficial in hypertensive type 2 diabetic subjects with insulin resistance. The hemodynamic effects of ACE inhibitors are associated with enhanced levels of the vasodilator bradykinin and decreased production of the vasoconstrictor and growth factor angiotensin II (ATII). In insulin-resistant conditions, ACE inhibitors can also enhance whole-body glucose disposal and glucose transport activity in skeletal muscle. This review will focus on the metabolic consequences of ACE inhibition in insulin resistance. At the cellular level, ACE inhibitors acutely enhance glucose uptake in insulin-resistant skeletal muscle via two mechanisms. One mechanism involves the action of bradykinin, acting through bradykinin B(2) receptors, to increase nitric oxide (NO) production and ultimately enhance glucose transport. A second mechanism involves diminution of the inhibitory effects of ATII, acting through AT(1) receptors, on the skeletal muscle glucose transport system. The acute actions of ACE inhibitors on skeletal muscle glucose transport are associated with upregulation of insulin signaling, including enhanced IRS-1 tyrosine phosphorylation and phosphatidylinositol-3-kinase activity, and ultimately with increased cell-surface GLUT-4 glucose transporter protein. Chronic administration of ACE inhibitors or AT(1) antagonists to insulin-resistant rodents can increase protein expression of GLUT-4 in skeletal muscle and myocardium. These data support the concept that ACE inhibitors can beneficially modulate glucose control in insulin-resistant states, possibly through a NO-dependent effect of bradykinin and/or antagonism of ATII action on skeletal muscle.

Vasopeptidase inhibitor omapatrilat induces profound insulin sensitization and increases myocardial glucose uptake in Zucker fatty rats: Studies comparing a vasopeptidase inhibitor, angiotensin-converting enzyme inhibitor, and angiotensin II type I receptor blocker

BACKGROUND

ACE inhibitors (ACEIs) improve insulin resistance and prevent type 2 diabetes, possibly mediated by inhibition of bradykinin (BK) degradation. The vasopeptidase inhibitor omapatrilat (OMA) raises BK to a greater extent than ACEIs by dual enzyme inhibition, whereas its insulin-sensitizing effects and mechanisms have not been investigated.

METHODS AND RESULTS

We compared the insulin-sensitizing effects of OMA, ramipril (an ACEI), losartan (an angiotensin II type 1 receptor blocker), and placebo by 2-step euglycemic hyperinsulinemic clamp in insulin-resistant Zucker fatty rats (n=6 to 7 in each group). OMA resulted in a lower rate of endogenous glucose production than placebo at baseline (35+/-5 versus 54+/-4 mmol x kg(-1) x min(-1), P<0.01), greater suppression of endogenous glucose production by low-dose insulin (73+/-11% versus 27+/-18%, P<0.05), and greater glucose disposal at high-dose insulin (135+/-5 versus 92+/-4 mmol x kg(-1) x min(-1), P<0.01). Ramipril tended to improve insulin sensitivity, but losartan did not. OMA significantly increased 2-deoxyglucose uptake by myocardium, fat, and skeletal muscle. Ramipril increased 2-deoxyglucose uptake only by some skeletal muscles, but losartan did not. The insulin-sensitizing effects of OMA were blocked significantly by HOE-140 (a BK, B2 receptor antagonist) and NG-nitro-L-arginine methyl ester (a nitric oxide synthase inhibitor) in all tissues except myocardium.

CONCLUSIONS

OMA induces profound insulin sensitization and increases myocardial glucose uptake in Zucker fatty rats. This effect is greater than that of ramipril and probably occurs at least in part via stimulation of the B2 receptor. OMA has the potential for greater type 2 diabetes prevention than ACEI.

Effects of dual angiotensin-converting enzyme and neutral endopeptidase 24-11 chronic inhibition by mixanpril on insulin sensitivity in lean and obese Zucker rats

The aim of this study was to examine the effects of chronic (8-day) oral treatment with the dual angiotensin-converting enzyme (ACE) and neutral endopeptidase 24-11 (NEP) inhibitor mixanpril (25 mg/kg twice a day), compared with the ACE inhibitor captopril (25 mg/kg twice a day), on whole body insulin-mediated glucose disposal in young (10-week) and old (19-week) obese Zucker rats (ZOs). Moreover, the effects of chronic mixanpril administration on femoral blood flow at rest and during an insulin infusion were assessed. In the young ZOs, mixanpril decreased the glucose response during an IV glucose tolerance test more effectively than did captopril (-49 and -30%, respectively, p < 0.05). Incremental glucose area under the curve in mixanpril-treated ZOs was then no longer different from that observed in vehicle-treated lean rats (1,592 +/- 175 and 1, 470 +/- 104 mg/dl x min, respectively). The beneficial effects resulting from mixanpril or captopril administration were observed in ZOs but not in lean littermates. In the old ZOs, mixanpril induced higher glucose infusion rates to maintain euglycemia than did captopril during a hyperinsulinemic euglycemic clamp test (+92 and +35%, respectively, p < 0.001). However, the glucose infusion rates in mixanpril-treated ZOs remained much lower than that observed in vehicle-treated lean rats (9.4 +/- 0.7 mg/kg/min vs 28.6 +/- 1.0 mg/kg/min, p < 0.001). Mixanpril did not affect resting femoral vascular bed hemodynamics but restored the femoral blood flow response to insulin infusion. In conclusion, in ZOs, chronic dual ACE/NEP inhibition improves whole body insulin-mediated glucose disposal more effectively than does ACE inhibition alone. This beneficial effect seems to be restricted to conditions of insulin resistance and not directly linked to the improvement in the femoral blood flow response to insulin.

Dual ACE and Neutral Endopeptidase Inhibitors

Elevated blood pressure is a risk factor for a variety of cardiovascular disorders, including coronary heart disease, peripheral vascular disease, cardiac failure and cerebrovascular disease. The prevailing view is that an elevated systolic rather than diastolic blood pressure is the major contributor in mortality and morbidity attributed to cardiovascular disorders. Isolated high systolic blood pressure, especially in the elderly, is a major risk factor and should undoubtedly be a target for drug treatment. In the general population, systolic and diastolic blood pressure are highly correlated, and thus it is difficult to dissociate the effects of these two components of the blood pressure and specifically ascribe cardiovascular risk factors to just elevated systolic blood pressure. Therefore, the goal in therapy of an individual with hypertension must be to reduce elevated systolic and diastolic blood pressure in order to reduce mortality and morbidity. ACE and neutral peptidase inhibitors are a new class of drugs that may be beneficial in the treatment of patients with hypertension and heart failure. They may also be useful in the treatment of diabetic patients with hypertension and/or heart failure. Drugs of this class are dual inhibitors of ACE and neutral endopeptidase, and are capable of affecting vascular tone and fluid balance. They are capable of producing vasodilatation by virtue of inhibiting the production of angiotensin II, degradation of natriuretic peptides and bradykinin. They also appear to promote natriuresis and diuresis by amplifying the actions of natriuretic peptidase and reducing aldosterone effects. In addition, they should also attenuate trophogenic actions of the renin angiotensin system and the sympathetic nervous system. Omapatrilat is one drug that appears to be at the advanced stages of clinical development. This drug has been shown to be quite effective in the treatment of hypertension. Evidence also seems to indicate that treatment with omapatrilat results in a higher tendency towards preventing death and worsening heart failure when compared with treatment with a pure ACE inhibitor in patients with advanced heart failure. Overall safety with omapatrilat appears to be good, but like other ACE inhibitors the incidence of cough is higher when compared with placebo. Other common adverse effects noted are headaches, facial flushing/warm sensation, dizziness, nausea and dyspnoea. Of greater concern is the occurrence of angio-oedema, the true incidence of which remains to be fully established as part of the published medical literature.

The role of the angiotensin system in cardiac glucose homeostasis: therapeutic implications

Resistance to the metabolic actions of insulin is thought to play a determining role in the aetiology of a great variety of disorders, including essential hypertension, accelerated atherosclerosis and cardiomyopathies. ACE inhibitors are recognised as being highly effective therapy for hypertension and cardiac insufficiency, and have a more beneficial effect on survival rate than expected on the basis of known mechanisms of action. The mechanism responsible for these extremely positive effects are just beginning to be understood and appear to be linked to the effects these drugs have on metabolism. The relationship between the insulin and angiotensin II (Ang II) signalling pathways needs to be fully clarified in order to prevent or correct the target organ damage resulting from changes in the cross-talk of these two hormonal systems. In recent years, Ang II has been shown to play a central role in cardiovascular and neuroendocrine physiology as well as in cellular cycle control. Moreover, the fact that Ang II utilises the insulin-receptor substrate (IRS)-1 to relay signals towards their intracellular destination, provides the biochemical explanation of how these two systems interact in a healthy organism and in a diseased one. Since it is overactivity of the renin-angiotensin system that seems to impair the intracellular response to insulin signalling, cardiovascular drugs that modulate the cellular transmission of Ang II have attracted particular interest. As well as the already widely-used ACE inhibitors, selective blockers of the Ang II type 1 receptor (AT(1)) have been shown to be clinically effective in the control of haemodynamic parameters, but with perhaps a less striking effect on glucose homeostasis. Many trials have investigated the effect of Ang II blockade on systemic glucose homeostasis. The inhibition of Ang II by ACE-inhibitors frequently showed a positive effect on glycaemia and insulin sensitivity, while information on the effects of AT(1) receptor antagonists on glucose homeostasis is more limited and controversial. An important limitation of these studies has been the short treatment and follow-up periods, even for the 'so called' long-term studies which were only 6 months. Several investigators have focused on the effects of the nuclear factors involved in gene transcriptions, especially with respect to the agonists/antagonists of peroxisome proliferator-activated receptors (PPARs) and their intriguing interconnections with the insulin and Ang II subcellular pathways. In fact, in vitro and in vivo experimental studies have shown that thiazolidinediones (selective PPAR-gamma ligands) are not only powerful insulin sensitisers, but also have anti-hypertensive and anti-atherosclerotic properties. In addition to conventional pharmacological approaches, attempts have been made to use genetic transfer in the treatment of cardiovascular and metabolic disorders. The development of powerful viral vectors carrying target genes has allowed us to restore the expression/function of specific proteins involved in the cellular mechanism of insulin resistance, and research now needs to move beyond animal models. Although a clearer picture is now emerging of the pathophysiological interaction between insulin and Ang II, especially from pre-clinical studies, there is much to be done before experimental findings can be used in daily clinical practice.